The state of the art of implantable pulse generators for stimulating human tissue has advanced to the point that such devices are being designed and used in increasing numbers to treat a wide variety of medical conditions. In addition to implantable pulse generators for treating many different types of cardiac conditions (bradycardia, tachycardia, fibrillation, and the like), so-called neurological pulse generators have been provided for stimulating a patient's nervous system, in order to treat such diverse conditions as pain, motor impairment, incontinence, spasticity, tremor, and impotence, to name only a few.
In most cases, electrical stimulation pulses are conveyed from an implanted pulse generator to the desired stimulation site by means of an implanted lead having exposed electrodes at its distal end. In order to achieve the desired effects from delivery of stimulating pulses it is of course very important that the lead be properly positioned and stabilized in the patient, so that as much of the stimulating energy as possible is delivered to the appropriate site. While this is true for all kinds of stimulation pulse therapies, lead positioning is especially critical in the area of neurological pacing, such as when stimulation pulses are delivered by a lead positioned in the epidural space adjoining the patient's spinal column. Even if the initial lead placement is correct the problem of lead migration often occurs. The delicate and highly sensitive nature of the spinal column, and the possible harmful or otherwise undesirable effects of delivering stimulation pulses to an inappropriate site in this area accentuates the need for precise lead placement and the ability to stabilize or anchor the lead at the appropriate site.
Proper placement is also important in the positioning of catheters used in the injection or withdrawal of fluids from the body. If the proper location cannot be maintained the fluids may be introduced or withdrawn from the wrong location or other problems may be encountered. For example, a recurring problem encountered with catheters introduced into the intrathecal space is catheter migration. If the catheter slips out of the intrathecal space not only is the drug not delivered in the proper location but a leakage of spinal fluid may also occur.
Attempts have been made in the field of neurological stimulation to develop leads which overcome the problem of lead migration. One such lead is disclosed in U.S. Pat. No. 4,285,347 to Hess. Disclosed is an epidural electrode lead having a distal end portion with a resilient portion which is laterally extended when a stylet is not inserted. Insertion of the stylet operates to straighten the resilient portion so that it is no longer laterally extended. The lead is inserted into the spinal canal through a Touhy needle with the stylet inserted. When the distal end of the lead is properly located the stylet is removed and the resilient portion returns to its original laterally extended shape for the purpose of stabilizing the lead.
A biomedical lead utilizing a lobed lead anchor for stability is disclosed in U.S. Pat. No. 4,419,819 to Dickhudt, et al. The lobes are formed utilizing a length of tubing which is slit along a direction parallel to its axis. The tubing is slipped over the lead body and compressed so that the slit portions of the tubing expand into lobes. While the tubing is compressed its ends are fused to the lead body, thus producing a biomedical lead having four curved lobes near its distal end. Again, the lead is inserted through a Touhy needle with a stylet inserted. Pressure in the distal direction on the stylet keeps the lobes retracted until the lead is properly located. Once the stylet is retracted the lobes expand outwardly to their preformed configuration to stabilize the lead.
In the field of cardiac pacing leads the use of an anchoring mechanism for anchoring the distal tip with respect to the inside of the heart is well known and very important to a successful pacing system. A widely used anchoring mechanism is that of tines, as disclosed in U.S. Pat. No. 3,902,501 to Citron, et al. The tined lead provides a plurality of pliant tines that extend from an area adjacent the distal tip of the leads, the tines forming an acute angle with the lead body. The tines are effective in engaging the trabeculae found in the ventricle as well as the atrium, to maintain the electrode tip in a secure position after the physician has positioned it for good pacing threshold. Other variations of the tined lead concept are disclosed in U.S. Pat. Nos. 4,913,164 to Greene et al., 4,957,118, to Erlebacher, and in German Patent Application 33 00 050.
The problem with these devices is that either they allow the physician only limited control over the anchoring mechanism when they are being inserted or they are very complicated both in terms of construction and use. In most the physician must rely on the "memory" of the tines, lobes or other anchoring configuration to secure the lead once the stylet is removed. Although some leads such as those disclosed in U.S. Pat. Nos. 4,913,164 and 4,957,118 provide the physician with control over both extension and retraction of the tines, the mechanisms rely on a complex strut system which is both difficult to operate and to manufacture. Additionally, once the leads are implanted for any length of time tissue ingrowth would make the tines difficult to retract.
In order to overcome the problems associated with present anchoring mechanisms it can thus be seen that there is a need for a lead having an easy to use anchoring mechanism which provides the physician with control over both extension and retraction of the mechanism while at the same time eliminating the complex structure associated with present leads.